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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

CO2 lags temperature - what does it mean?

What the science says...

When the Earth comes out of an ice age, the warming is not initiated by CO2 but by changes in the Earth's orbit. The warming causes the oceans to release CO2. The CO2 amplifies the warming and mixes through the atmosphere, spreading warming throughout the planet. So CO2 causes warming AND rising temperature causes CO2 rise. Overall, about 90% of the global warming occurs after the CO2 increase.

Climate Myth...

CO2 lags temperature
"An article in Science magazine illustrated that a rise in carbon dioxide did not precede a rise in temperatures, but actually lagged behind temperature rises by 200 to 1000 years. A rise in carbon dioxide levels could not have caused a rise in temperature if it followed the temperature." (Joe Barton)

Over the last half million years, our climate has experienced long ice ages regularly punctuated by brief warm periods called interglacials. Atmospheric carbon dioxide closely matches the cycle, increasing by around 80 to 100 parts per million as Antarctic temperatures warm up to 10°C. However, when you look closer, CO2 actually lags Antarctic temperature changes by around 1,000 years. While this result was predicted two decades ago (Lorius 1990), it still surprises and confuses many. Does warming cause CO2 rise or the other way around? In actuality, the answer is both.

Interglacials come along approximately every 100,000 years. This is called the Milankovitch cycle, brought on by changes in the Earth's orbit. There are three main changes to the earth's orbit. The shape of the Earth's orbit around the sun (eccentricity) varies between an ellipse to a more circular shape. The earth's axis is tilted relative to the sun at around 23°. This tilt oscillates between 22.5° and 24.5° (obliquity). As the earth spins around it's axis, the axis wobbles from pointing towards the North Star to pointing at the star Vega (precession).

Figure 2: The three main orbital variations. Eccentricity: changes in the shape of the Earth’s orbit.Obliquity: changes in the tilt of the Earth’s rotational axis. Precession: wobbles in the Earth’s rotational axis.

The combined effect of these orbital cycles causes long term changes in the amount of sunlight hitting the earth at different seasons, particularly at high latitudes. For example, the orbital cycles triggered warming at high latittudes approximately 19,000 years ago, causing large amounts of ice to melt, flooding the oceans with fresh water. This influx of fresh water then disrupted the Atlantic meridional overturning circulation (AMOC), in turn causing a seesawing of heat between the hemispheres (Shakun 2012). The Southern Hemisphere and its oceans warmed first, starting about 18,000 years ago. As the Southern Ocean warms, the solubility of CO2 in water falls (Martin 2005). This causes the oceans to give up more CO2, emitting it into the atmosphere. The exact mechanism of how the deep ocean gives up its CO2 is not fully understood but believed to be related to vertical ocean mixing (Toggweiler 1999).

The outgassing of CO2 from the ocean has several effects. The increased CO2 in the atmosphere amplifies the original warming. The relatively weak forcing from Milankovitch cycles is insufficient to cause the dramatic temperature change taking our climate out of an ice age (this period is called a deglaciation). However, the amplifying effect of CO2 is consistent with the observed warming.

CO2 from the Southern Ocean also mixes through the atmosphere, spreading the warming north (Cuffey 2001). Tropical marine sediments record warming in the tropics around 1000 years after Antarctic warming, around the same time as the CO2 rise (Stott 2007). Ice cores in Greenland find that warming in the Northern Hemisphere lags the Antarctic CO2 rise (Caillon 2003).

To claim that the CO2 lag disproves the warming effect of CO2 displays a lack of understanding of the processes that drive Milankovitch cycles. A review of the peer reviewed research into past periods of deglaciation tells us several things:

Deglaciation is not initiated by CO2 but by orbital cycles

CO2 amplifies the warming which cannot be explained by orbital cycles alone

CO2 spreads warming throughout the planet

Overall, more than 90% of the glacial-interglacial warming occurs after the atmospheric CO2 increase (Figure 3).

Further reading

"Changes in the CO2 and CH4 content have played a significant part in the glacial-interglacial climate changes by amplifying, together with the growth and decay of the Northern Hemisphere ice sheets, the relatively weak orbital forcing"

The paper also notes that orbital changes are one initial cause for ice ages. This was published over a decade before ice core records were accurate enough to confirm a CO2 lag (thanks to John Mashey for the tip).

Further viewing

Comments

Nice correlation between T and CO2 level. However, given a correlation between two variables one has still to clarify which is doing what.
One might of course notice that in the most recent "burst" CO2 gets well above the temperature curve, unlike the previous cases.
Does anyone know what in the past produced the "fast" T and CO2 growths?
Marco

It is reasonable that warming of the oceans is in fact causing CO2 increase in the paleo record. What I wonder about is how anyone can turn this into evidence that CO2 causes warming?

When I first saw this at an ACS function nearly 20 years ago these curves were presented as proof of CO2 caused warming; despite the obvious fact that the graphs, even then, showed that the temperature change was not following but rather was leading the CO2 change. Now we are trying to explain away T changing first invoking creative models. It appears the fundamental premise that CO2 causes warming is simply not supported by the paleo record. It may still be true, but what evidence do we have in the climate record that supports this hypothesis?

Here is another question: If ice ages are on 100,000 year cycles because the Earth's orbit is more elongated on 100,000 year cycles why is the Earth's orbit so round now? Shouldn't it be nearing maximum excentricity?

Response: The paleo record shows that Antarctic temperatures rise about ~800 years before CO2 and Greenland temperatures rise after the CO2 rise. The CO2 warming effect is necessary to explain both how weak orbital forcing can get us out of an ice age and also how an orbital forcing that affects only southern areas can spread through the globe. The paleo record also enables us to compare Co2 forcing with temperature change to calculate climate sensitivity.

RE: response
Are we sure about that? I am sure the original data from way back then was actually from Greenland ice cores, showing that temperature was rising before CO2, there as well as in the Antarctic. The Antarctic data was not yet around. If CO2 is rising first in Greenland than your hypothesis may be correct. I know CO2 is supposed to cause warming, and I think I understand why. But, the data still seems to scream corelation does not equal cause and effect.

Response: The "original data from way back then" was probably Monnin 2001 which used the Dome Concordia ice core or Caillon 2003 which used the Vostok core - both are from Antarctica. Caillon concludes "The sequence of events during Termination III suggests that the CO2 increase lagged Antarctic deglacial warming by 800 ± 200 years and preceded the Northern Hemisphere deglaciation." More recently, Stott 2007 found that tropical temperatures lag southern warming by ~1000 years. I agree with you - correlation does not necessarily imply causation. But the ice core record is consistent with the warming effect of CO2 and explains both the degree of deglaciation and how a localised warming (increased insolation in the south) spread across the globe.

No, the American Chemical Society Conference at which I noted this discrepency in a presented paper was in 1989 because I was in Grad Chemistry courses at the time, so I much doubt that it was 2001 or 2003 data. Other than that I hope you're right because otherwise 1)we are being led down the primrose path and 2) I am freezing my butt off up here.

The presenter after having this error spotted by a lowly physics type grad student was not well recieved in the question session by the roomful of chemistry PhD's that were present. None the less his hypothesis that CO2 causes global warming is still widely discussed. :)

Response: I would be surprised if ice core records were of sufficient resolution back in 1989 to clarify CO2 was lagging temperature - it's only been more recent ice core records that have been of high enough resolution to clarify the CO2 lag. Spencer Weart has published a great online history of ice core measurements that is well worth a read.

Without knowing which older studies you're talking about, the most recent studies with up to date (and dare I say the most accurate) data (Monnin 2001, Caillon 2003) paint a similar picture of Southern warming -> CO2 rise -> Northern warming. But if you do know of any pertinent older papers, it'd be great if you could post the links here. And kudos for sticking it to the man :-)

First of all, John, thanks for spending the time to create and maintain this site. I do realize it must be quite substantial time commitment. Although, it is not exactly neutral and is somewhat driven by your current opinion that GW is mostly due to anthropogenic CO2 emissions, the forums on the site are still one of the few places where we can have some more meaningful debates based on some scientific thinking and facts. So, in some respect the website is just like Churchill's quote on democracy (I think, he is the right man to quote since as you've correctly noticed many things in the GW debates on both sides are politically motivated consciously or not):

"It has been said that democracy is the worst form of government except all the others that have been tried. "

Of course there are another two quotes from him that I think very much apply to the GW debate:

"The best argument against democracy is a five-minute conversation with the average voter. "

&

"A lie gets halfway around the world before the truth has a chance to get its pants on."

Well, enogh quotes. On a more serious note, sadly enough, the whole field of Climate Science and Global Warming has become just like Finance. There is so much easy money flowing around that there is a great number of people with all sorts of backgrounds and levels of knowledge that have no relation to climate/physics or anything distinctly related (although by all means I am not saying we should only used established scientists' work as a guideline) that would make most outrageous claims/predictions with arbitrary certainty backed up many low-quality science booklets/papers/reports, posh presentations and heavy media support to streer more funds their way. In general, what I'm refering to is the so-called "press release science", unfortunately endemic to so many other fields besides climate.

And finally, refering to the following quote from your bio section:

"I'm still yet to meet a skeptic argument that is even vaguely convincing."

I would suggest looking at some arguments that come from people that don't exactly fit the typical skeptic stereotype you describe, for example take a look at this list
http://www.warwickhughes.com/hoyt/climate-change.htm

and the following scorecard on the same website
http://www.warwickhughes.com/hoyt/scorecard.htm

Response: Love those quotes from Churchill. I must confess, I'm not particularly impressed with Warwich Hughes' climate change page which reads a lot like my Skeptic Arguments page (except mine is more comprehensive :-) His scorecard is interesting - if I have more time after maintaining this site (and responding to your comments), I'll give it a closer look.

All of the conclusions you make in your rebuttal of the skeptics argument are valid only if the Milankovitch cycles (which as you note provide relatively weak forcing) are indeed the sole cause for this whole process. This seems like a big assumption to me and I don't think the science behind that has been settled. Most of people sort of automatically assume it, but there are number of scientists starting with John Imbrie (the guy who led the whole CLIMAP effort and published the infamous Ice Ages: Solving the Mystery) that say Milankovich cycles (Earth's orbital variations and such) seem to explain only 50-60% of the whole insolation variance. So, adjusting one's model only using insulation curves generated by orbital modeling as they do in the papers you mention seems unjustified to me. In essence, the authors of the above papers precondition themselves to look only for models that fits their believes (that are only limited to Milankovich cycles as a driver). There are many other additional hypothesis that also make sense even though their quantification is not as simple as just writing an orbital mechanics models which is all nice and simple with nice math functions. A major examples for additional forcings on these time scales include changes in the solar irradiation due to the long-term manifestations of the solar activity that are ought to be much bigger that what we've observed with satellites for the past 20 years (I refer to the TSI measurements) and are not only related to the TSI, but to things like the solar diameter, the solar wind and its interactions with Earth's magnetic field and many other process on the Sun and inside the Earth's core. Many things in the Solar System seem to work in synergy. So, that many cycles and superpositions of cycles of completely different physical processes external or internal to the Earth's climate have similar length and appear as if only one factor is at work when in fact there are several. I acknowledge that there is the Occam's razor that advocates simplicity, but I don't necesesarily think it is the best approach when we are considering Earth's climate and the near-Earth environment.

So, I wasn't really asking about the lags, but whether we can even begin to consider that these lags mean anything. As far as the error bars, I was asking for the errors of the reconstruction models that create those curves on the graphs you show. The lines only follow the positions of the 50% quantile of each model output point but tell us nothing about its possible range (due to original measurement errors and other uncertainties).

Response: There's still a lot to be worked out re the whole mechanism of deglaciations. For example, there are various theories on what causes the CO2 increase after temperature increase, the most accepted theory being degassing from the deep ocean. I've read of theories that the 100,000 year cycle is caused by solar variations rather than orbital changes although the Milankovitch theory seems to be more established and confirmed by at least several papers I've read. But the main point of this page is to answer the argument that "the CO2 lag debunks anthropogenic global warming". The current scientific understanding of the CO2 record (and the papers quoted in citing CO2 lag) state that the CO2 lag confirms the warming effect of well mixed atmospheric CO2.

This discussion goes on as if the only evidence we have to decide whether CO2 has a warming effect is the paleoclimate data. That's a very, very narrow perspective.
What everyone needs to appreciate is that we have fundamental physics and really, really extensive laboratory analysis of the absorption spectra gases alone and in combination, at all sorts of temperatures and pressures. You can look up the raw data on HITRAN at http://www.cfa.harvard.edu/hitran/ and you can read the conclusions drawn from this raw data about the greenhouse effect at, e.g. Ray Pierrehumbert's free access draft of his "Climate Book" http://geosci.uchicago.edu/~rtp1/ClimateBook/ClimateBook.html

This is a university level physics textbook, not aimed at the general public. If you need more basic accounts of how GHGs absorb infrared, you can check out www.realclimate.org where Dr. Pierrehumbert is an active contributor. I'm linking to the academic text just to point out that belief in CO2 being a greenhouse gas, able to *cause* warming as well as respond to warming, is built on over a century of physics and lab analysis, and really, really NOT just on a few graphs taken from ice cores and put up on the screen by Al Gore.
Way too much online discussion has treated this as if the whole line of reasoning rested solely on the paleo graphs and nothing else.
To sum it up: temperature changes do indeed drive CO2 changes, *and vice versa*. The positive feedback between the two accounts for how ice age terminations get moving so much faster than the very gradual Milankovic forcings. The feedbacks don't run away forever because, for one, the carbon dissolved in the ocean is not infinite, the ice albedo feedback runs out when the glaciers and sea ice have retreated, etc.

Response: Thanks, very pertinent comment and the link to Pierrehumbert's page is useful, particularly the latest draft of his upcoming Textbook on climate. Down the track, I hope to update this page fleshing out the point that CO2 warming is not dependent on ice core records but on fundamental physics (yet another on the to-do list :-)

I have two questions regarding this "CO2 lags temperature" argument. You say that the Milankovitch cycle is to weak to explain the big temperature difference and that it requires strengthening through energy absorption by means of CO2. How do we know that CO2 is the main cause and not something else, e.g., the change in Earth's albedo due to ice and snowcover ?

Also you say that it is not fully understood how oceans give up CO2. What about the reverse, the removal of CO2 from the atmosphere when the Milankovitch cycle drives the temperature down ?

This idea that Malinkovitch needs CO2 feedback to do the job is clearly false. Since it relies on a WATTS-PER-SQUARE-METRE model which is a light-and-air-only model.

If we allow for the accumulation and decumulation of joules in the planet and the oceans then it is the factor of TIME ALONE that needs to be taken into account and not this sideshow of CO2-feedback.

We ought to be looking at a model which relies on STRATA AND HEAT BUDGETS.

Not on WPSM. The WPSM model is a first draught that people came up with looking through telescopes. They couldn't see anything else so they imagined the whole thing could be determined by spectroscopy alone. But what we are talking about is the accumulation and decumulation of joules.

Another thing that these WPSM models fail to take into account is the distance travelled through the atmosphere.

The stratosphere ends about 50km up in the air. But that doesn't mean that a "ray" of light hitting the stratosphere has to travel only 50km.

This is only true at the equator and at high noon. And this is important since the climate guys talk as if only greenhouse gas and ozone can attenuate this radiation. But all gasses inhibit radiation and a lot of this radiation has a very long way to go.

Not taking into account of this and failing to think about ACCUMULATION and DECUMULATION of joules over many decades and years is a fatal flaw to these climate models.

Actually, Milankovitch hypothesis requires much more than WATTS_PER_SQUARE_METRE. The thing is that GLOBAL year-average solar flux does not change more than 0.1% during those cycles. Climatologists like to plot amplitude of "Milankovitch forcing" at one spot on Earth - at latitude 65N, which does not represent in any way or form the GLOBAL change in incoming radiation. I find this very misleading, especially when the whole talk is about GLOBAL warming. For the Milankovitch to have any effect on Earth, climatologists have to use a hidden assumption that Nothern Hemishpere controls the whole climate by having some sort of "rectifier effect". So far this rectifier has not been identified, and ony speculations exist that it has something to do with more land in NH than in SH, and maybe with Arctic ice having contact with land (Greenland etc).

birdbrainscan wrote: "What everyone needs to appreciate is that we have fundamental physics and really, really extensive laboratory analysis of the absorption spectra gases alone and in combination, at all sorts of temperatures and pressures. You can look up the raw data on HITRAN at http://www.cfa.harvard.edu/hitran/ and you can read the conclusions drawn from this raw data about the greenhouse effect at, e.g. Ray Pierrehumbert's free access draft of his "Climate Book""

I am familiar with this book, it is really a university level physics textbook, under which I mean "entry level". One needs to realize that the explanation of GH effect inherently relies upon so-called "atmospheric lapse rate", to link the height of "effective emission layer" with surface temperatures. One really needs to realize that so-called "lapse rate" must be an average of all atmospheric structures and weather patterns over the whole globe and from ground up to the whole troposphere. One needs to realize that the atmospheric patterns include turbulent boundary layer, global circulation patterns (Hadley, Ferrel, and polar cells), jet streams, hurricanes and other tropical depressions. More importantly, the lapse rate is strongly affected by moisture, which, in turn, is strongly affected by sea temperature. What is more important is that the moisture tends to condense into clouds under certain atmospheric/aerosols conditions. The laps rate ("moisture adiabate") tends to DECREASE with higher moisture content providing a negative feedback. Clouds also provide negative feedback by reducing insolation.

Needless to say that all of listed processes occur under strong non-isotropic turbulent conditions, and are way beyond the reach of any direct computer modeling. As result, either a hand-made parameterizations have to be used, or parameterizations of experimental data. Given the spatio-temporal complexity of atmospheric patterns, data from few weather balloons cannot be seriously considered as a good representation of average atmospheric structure. The reference to HITRAN/MODTRAN serves no purpose for this discussion since the code uses a pre-selected fixed MODEL of atmospheric profile. In MODTRAN, there are 84 different models for atmospheric profiles; each gives different result for amount of OLR and surface temperature. So, what would be your selection of models across the globe to include into a global greenhouse model? How objective or subjective it could be? As you see, the "fundamental physics" of absorption spectra or two-stream Schwarzschild equations are not all the sophistications you need to build a model of GH effect and calculate its amplitude.

Tekhasski, you sure can pile on the jargon but the basic argument is not affected by what you or GMB are saying: sunlight comes in with a small amount of long-wavelength infrared (so does not get absorbed so much by CO2, methane, NO2, etc.), gets absorbed, then tries to head out again as blackbody radiation, which is mostly in the long-infrared range and is strongly absorbed by the accumulating CO2, methane, NO2, etc. in the atmosphere.

No matter what the atmosphere is doing, if you add heat you get warming. You don't need a PhD to understand that.

The main outcome of the above research is to suggest that heating of the planet causes more carbon dioxide in the atmosphere (with some delay). We already know that increased carbon dioxide causes warming, so this means that the warming will be amplified by increased CO2 emission from the oceans.

GMB, everything you are saying has already been taken into account in the current climate models.

Climatologists have been out of their armchairs for decades now; where are you sitting?

Nice personal attack Farmer but it added nothing to this discussion. Your Comment "No matter what the atmosphere is doing, if you add heat you get warming. You don't need a PhD to understand that." makes no sense in this context.

There is no heat being added unless you are talking about variation in Solar output. The warming is supposed to be the result of Earth holding on to more heat and releasing it more slowly. The Earth is not a Black body radiator, but that doesn't even matter because CO2 isn't a big absorber of black body radiation at this temperature.

Or this comment "We already know that increased carbon dioxide causes warming, so this means that the warming will be amplified by increased CO2 emission from the oceans."

This is simply not correct. We think it should work this way, we have some theoretical reason to believe it should. But, it has rather badly failed the experimental test so far. In addition if your assertion were true this would be a positive feedback loop that is clearly not present in the Earth's paleo record. If the climate really worked this way the Earth would be vastly warmer than it is and would never have had any ice ages because once the CO2 got high, as it has many times in the past, it would cause a warming spiral.

The idea that you can "take into account" in models affects that we simply don't understand is absolutely silly.

What if CO2 is meaningless? The graphs show measured concentrations of CO2 for the past how many years? Modern direct measurement of gases using a bench and means of interpreting past CO2 are not going to give the same results. Even trapped gas pockets in ice suffer from osmotic action. Past climates are mostly guesswork. As Wondering Aloud points out "it would cause a warming spiral." but that did not happen. The graph shows 450K years, ALL of which were within the oscillations of an ice age. We assume that this is an interglacial period. What if it isn't? How do we know that the planet isn't returning to Earth Normal or Earth Mean temperature? The fact is, we don't know.

Quietman
'How do we know that the planet isn't returning to Earth Normal or Earth Mean temperature?'

Are you seriously proposing a new theory - that the Earth has a memory? Do you have a mechanism? Or a 'setting' to which this 'memory' is adjusted? Is there any peer-reviewed literature as a source?

CO2 clearly cannot be meaningless, it has long been known to be infra-red active and remains resident in the atmosphere for a long time, from memory ~33% remains after one hundred years and 20% after a thousand years, but there is a long tail meaning that some will remain for tens of thousands of years, causing significant warming. Inevitably, this alone will affect the net heat balance of the Earth. Of course CO2 is NOT the only GHG and as temperature increases, so does the water vapour, which acts as a positive feedback amplification. But while water vapour is a stronger GHG than CO2, it does not remain in the atmosphere for long.

The source of the excess CO2 is explained by the shifting isotopic ratio of the atmospheric carbon. From this it is known to originate from non-biological sources - i.e. fossil carbon: coal, oil & gas.

Sorry, but I couldn't locate a version in the p/r literature. I've seen them before, it's just that I couldn't find any.

We are clearly performing a global experiment and no-one can be absolutely certain as to the precise outcome, but if it does all go dreadfully wrong, the trouble is that we are INSIDE the test-tube!

It would therefore be a really good idea to heed the scientists and stop trying to light the Bunsen burner!

Let's cut-back on the use of fossil-fuels, through improved technology, energy conservation & efficiency and renewable energy generation.

The economic argument that carbon taxes will damage the US economy is bogus.
“As Congress prepares to debate new legislation to address the threat of climate change, opponents claim that the costs of adopting the leading proposals would be ruinous to the U.S. economy. The world’s leading economists who have studied the issue say that’s wrong”
http://www.cis.yale.edu/opa/newsr/08-03-19-02.all.html

We owe it to the next generation and generations to come to hand over the Earth in the same condition as it was when we received it. Sadly, this will not be the case.

Response: Note - globalwarmingart.com usually cites his sources if you want to track down the original studies where he get the data from.

Quietman,
Another thought: Those graphs in my previous post show a rapid upward acceleration of CO2 in recent decades, one that matches the accelerated warming. If what you suggest were true: namely that Earth is [your hypothesis] 'returning' to 'normal', then one would expect an ever decreasing asymptotic approach. Instead, what is seen in the second graph is a rapid departure upwards from the upper bound historic values - the exact reverse of what is expected.

During a glacial period (between interglacials), the graph shows many changes in temperature direction, trend up, followed by trend down, followed by trend up, followed by trend down and so on for many cycles. If the theory is that a trend up causes atmospheric carbon dioxide to increase which adds to warming, why, with atmospheric carbon dioxide level higher than it had been during the temperature increase, would the temperature stop going up and go down instead?

ScaredAmoeba
1. I said "what IF. (food for thought). There is a CO2 feedback effect and a contribution by AGW regardless.
2. Not one single graph that I have seen matched the rise in CO2 to the rise in temperature without some serious manipulation.
Show me a graph of rising surface temperaturs that is based solely on rural weather stations and a chart of CO2 with a matching slope. You won't be able to.

ScaredAmoeba
Re: "The economic argument that carbon taxes will damage the US economy is bogus."
This is an unknown. It could go either way depending on exactly who is taxed and how much as well as who is hired and how many. If we are heavily taxed to pay for green products made in India we loose. If we are lightly taxed for production within the US by non-illegals we win. Can you assure us that the latter will be the case rather than the former?

In johns skeptic of the week article it says "Moreover, the Earth has experienced no discernible temperature increase since 1998, nearly nine years ago. Remember, too, that the atmosphere is approaching CO2 saturation--after which more CO2 will have no added climate forcing power." This I don't understand. Is this at all credible?

If you are refering to the saturation idea, credible yes, possible yes, right? I just don't know. It does look to me like most of the forcing predicted from a doubling of CO2 should have already occured unless there is a big time lag in the system that is un accounted for. this is why I asked on other threads if there was a lag of perhaps 30 years we didn't have identified. Without it we are down to only those large, but not now apparent, feedback numbers or a relatively small total signal on the order of 1 C.

I am a layman, but I thought that there was supposed to be more temperature increase in the troposphere (I think) rather than at the surface if the driving force behind rising temperatures was really CO2 levels.

In fact I am told the reverse has actually been observed. Doesn't this suggest that something other than CO2 has driven most or all of the warming of the last 30-40 years?

Response: RSS satellite data of troposphere temperature shows good agreement with models, having a slightly larger warming trend than the surface. UAH data has a slightly lower warming trend. The difference is due to how they adjust their data. What we expect to see in the troposphere and what we observe is within data uncertainty.

But this isn't supportive to the greenhouse hypothesis though is it? An absence of statistically signifcant readings on a measure that is quite central to the mechanism of how a phenomenon works can be blamed on poor data, of course, but this absence while providing no particular support to the contrary, doesn't exactly provide positive support to the greenhouse argment.

Or is it possible to say with some confidence that one of these two data sets is better than the other? (Although even the "supportive" data set is not able to disprove the null hypothesis of no greenhouse effect from what you say.)

[Apologies if this was the wrong page on the site to have raised this subject - at the time I began I didn't realise how extensive the site was].

I've tried to understand how the paleo ice records are anything more than anecdotal. Problem is I've seen counterveiling studies that show that light oxygen - a direct proxy for water vapor - shows a more-consistent correlation with paleo temperatures than CO2.

The ice ages hit an arid maximum and the thaws always saw a large increase in humidity as ice-locked water was returned to the hydrological cycle.

It makes sense that CO2 played a role in the interglacials but the discontinuities I see in the record seem to disprove an absolute temperature-driving record for CO2.

I mentioned the same thing on Watts' blog:

Take a look at this Vostok ice core:

http://www.ourworldfoundation.org.uk/IceCores1.gif

The CO2 levels associated with past interglacials is 180 to 300 ppm, well below where we are now.

325 kya when CO2 went from 200 to 310 ppm, what did the temperature trend show? It shot up 3 or more degrees, didn’t it? The problem is that contemporary CO2 levels were already at 280 ppm during the Little Ice Age and have risen to 385 ppm; however, we’ve yet to see any hint of an equivalent temperature trend, not even latent heat in the seas (oh sure, there’s some, but it’s not piling up at the rate predicted).

If you superimpose the light oxygen data (flip & stretch) over the past 200ky, (that’s easy to do even with MS Paint) you’ll see that the light oxygen trend line matches more closely to the paleo temperature trend than does the paleo CO2 trend where CO2 & temperatures periodically slip out of tight correlation (between 80 - 110kya and 160 - 180 kya).

http://i29.tinypic.com/28iyro8.jpg
( superimposition of the light oxygen chart over the vostok chart).

Eyeball analysis time: There are two discontinuities between CO2 & temperature that aren’t discontinuities between Light Oxygen and temperature.

Can you see the point? B/c of its evaporative and water-forming nature, light oxygen availability is a direct reflection of water vapor concentration in the atmosphere. So what’s the dominant driving agent? Is it CO2? Is it water vapor?

This is why climate agnostics aren’t won over by the pro-AGW paleoclimate studies, they seem anecdotal. If CO2’s effect were consistently strong (and it’s causes steeper temperature changes at lower concentrations) then temperatures would follow more closely to the CO2 line, but they don’t, temperatures follow the water vapor line (and vice versa). What CO2 effect there is is inconclusive.

CO2 may play a role, but it isn’t dominant throughout the paleo record. Just b/c it correlates doesn’t mean it causates.

Our current 380 ppm CO2 level isn’t reflected by the paleo data, contemporary CO2 levels have surpassed the level of spectral absorption that has been claimed to have caused that much warming in the paleo record. And the more CO2 is added to the air, the less additional effect it has in a trend of progressively diminishing returns.

Something’s inconsistent with the theory that CO2 drives temperatures.

“As Congress prepares to debate new legislation to address the threat of climate change, opponents claim that the costs of adopting the leading proposals would be ruinous to the U.S. economy. The world’s leading economists who have studied the issue say that’s wrong”

The world's leading economists? Have they mentioned the imbroglio brewing over in Europe, the ongoing rebellion in Britain?

In the EU the Europeans are looking at their carbon tax overheads and realizing that they could lose their steel firms to Asian steel makers. This is b/c of the market-distorting effect of carbon taxes levied on developed nations that are not levied on developing ones.

In England the additional green taxes saw "Red Ken" get ousted from the mayoral seat of London, where Ken Livingston saw the election as largely a green referendum. It was alright, an anti-green one. Labour is hammering Brown to relinquish some of the additional green taxes on trucking firms, etc.

Only three countries in Western Europe have met their Kyoto targets, Sweden & France using nuclear power and Switzerland from hydro.

And Japan - one of the most energy-efficient countries in the world - has simply said it cannot afford the Kyoto targets.

And a comment: I think what falls out of this is that CO2 is simply irrelevant, except insofar as it supports increased plant growth, and costs resources in a futile attempt to control it. If it made any difference, maximizing it to prevent Global Cooling would be a good idea, but ...

What about life? As temperature rises, so does metabolism..end result more plants/animals ( as long as other conditions allow) More plants, especially soft (non-woody) tissued, release more CO2. Plant decomposition accelerates adding methane to the atmosphere. temp goes up a bit more. CO2 rises a bit more, plants flourish. More ruminants = more methane, more CO2. Cycle continues until you start locking up CO2 in woody plants.
I'm not saying this is THE cause, but it is a factor to be considered and allows CO2 to lag T and then decline as forests develop (800 - 1000 years grows an awful lot of woody material)until (possibly!) CO2 levels begin to fall.
Also we should stop talking about variations in insolation being irrelevent. They aren't. The direct physical effect may be small...but the consequencies of that small effect may well be pretty big.

Mizimi
Astute observation. Much more credible than the "consensus" view as Methane actually is a GHG with more potential than CO2. But another factor is ocean and air currents that differ depending on location of the continents and locations of internal thermal forcing which I refer to as vulcanism (old habits die hard) that cause upwellings in the oceans constantly altering currents.

QM: Couldn't agree more. Climate records ( direct or proxy) indicate small changes until you get to some truly massive event...like an asteroid strike. This gives me comfort in the general stability of our climate; the issue then becomes one of degree. Any AGW effects have to be examined for the degree to which they may affect climate, not for the absolute change.
Oceanic currents, atmospheric currents are simply means of distributing/modulating heat flow; the whole system is a thermal model Heat in - Heat out which is modulated by a variety of factors ( and I don't like the use of the word 'forcing' because it carries other overtones) which we do not (yet) fully understand.
Incidentally, domesticated ruminants are estimated to produce 36Mtonnes of methane annually; the New Zealand government is introducing a 'emissions' tax on livestock farmers .........

Mizimi
The AGW argument here is based on the fact that TSI stopped following the temp curve in 75 or 76. And they are right on that account, it did. So we know solar forcing has the capability but what happened in 1975-76?
The single major event was a full (once in a lifetime) solar alignment. It won't happen again for a very long time. The results were not immediate but started within a few years of the event. The earth became active, plate movement increased speed, new volcanos appeared and old ones became active, large earthquakes, tsunamis and stronger ocean oscillations which are caused/controlled by vulcanism/tectonic activity.
In Dr. Fairbridge's hypothesis on gravity affecting the sun we can surmise that the effect would be strong enough to affect the earth as well, stirring things up, so to speak. This explains why only the northern pole is a problem and not the southern pole. It also explains the South Atlantic Magnetic Anomaly and why we had glacial melts. If you take into account all the anomalies since 1975 you start to see the pattern.

QM: I hear what you say and (as I have said in other places on this site) it simply re-inforces my view that the basic physical model still has some bits missing or not fully understood. We do not even have a reliable physical model for the fluid dynamics of the earth core, so how can you compute tectonic effects into the climate model that would have any real meaning?
As an aside: The moon causes tidal waves in all earth's material phases, and that effect is constantly modulated by the sun all the other planetary bodies.
I would not care to try and model that either!

Nevertheless, thank you everyone for a thoroughly scientific and impersonal debate on this topic. Its refreshing to read a thread like this minus all the politics and high emotion that usually comes with it

Austerlitz
The relationship as stated and accepted by the IPCC may indeed be false, I agree. But there is a feedback that has a minor effect and can be viewed as symptomatic. Spencer gives a good explanation for this, the sensitivity to CO2 is lower than the sensitivity of other drivers/forcings and easily overcome which is indicated in the current cooling trend. The idea that CO2 caused AGW therefore is rather meaningless since it is not strong enough to have driven climate change from 1975 through 2007. Recent articles on ocean oscillations and plate tectonics/vulcanism indicate that "The solar jerk" is at work.

Apparently climatologists do not have much grounding in how feedback works. Unaware of their ignorance, they invoke net positive feedback in their GCMs. This causes the GCMs to predict significant ‘enhanced global warming’. Anyone who has the ability and interest to look at the NOAA data from Vostok Ice Cores for the last glaciation (and prior glaciations) will discover that, repeatedly, a temperature increasing trend changed to a decreasing trend with the carbon dioxide level higher than it had been when the temperature was increasing. Graphs of NOAA and other credible data, all fully sourced so they can be verified, can be seen at http://www.middlebury.net/op-ed/pangburn.html. (The web site is controlled by Middlebury, not me.) Those who understand how feedback works will know that this temperature trend reversal is not possible with significant net positive feedback. Thus, as far as global climate is concerned and contrary to the assumption in the GCMs, significant net positive feedback from water vapor does not exist.

Response of the climate system depends on the combined effect of ALL feedbacks, known or not. When all are combined, the NET feedback can not be significantly positive. This is mandated by the temperature trend reversals of the last and previous glaciations. Without net positive feedback, the GCMs do not predict significant Global Warming. Other assessments from entirely different perspectives also determine that there is no significant net positive feedback. They can be seen at http://www.climate-skeptic.com/2008/01/index.html and http://www.weatherquestions.com/Roy-Spencer-on-global-warming.htm

You each dismiss the possibility of feedbacks to CO2-induced warming, without really explaining your problem. In each case this seems to relate to the observation that during Milankovitch cycles associated with glacial-interglacial-glacial transitions, the earth's temperature drops while atmospheric CO2 levels remain high for a while. But isn't that exactly what's expected if the CO2 rise and fall is itself a feedback from the primary (Milnkovitch-induced) warming?

Obviously atmospheric CO2 levels will lag behind temperature levels on both the rising and falling parts of the cycle. It's a question of relative magnitudes of forcings, and the timescales for various re-equilibration to changes in forcings. If the solar (insolation) dominates (as we consider to be the case), then it will "dominate" the effects of CO2, feedbacks and all.

We could make an analogy with the day night cycle. Right now atmospheric CO2 levels are the highest they've been for many millions of years and the Earth is warming. However last night while CO2 levels were extraordinarily high (382 ppm or whatever the current value is), when the sun went down, it got a bit cooler. In fact as the air cooled last night some of the water vapour precipitated out and it rained....

Now that scenario doesn't indicate that raised atmospheric CO2 doesn't have an associated positive water vapour feedback. It clearly does (we can measure this in the real world). It just means that the insolation effect dominates the CO2 effect, feedbacks and all.

The associated thing that needs to be considered is the timescale of the effects. The CO2 feedback to warming is very slow (and likewise to cooling). Once atmospheric CO2 levels are raised they stay that way for a long time. But both the warming effect of CO2 and its water vapour feedback are a consequence of an interaction with the insolation. If the insolation drops, then the greenhouse effect of the raised CO2 and water vapour will drop immediately. And a reduction in the feedbacks will follow on different timescales. The water vapour feedback will drop quickly (days to months following reduced warming resulting from reduced insolation)....the atmospheric CO2 levels will remain high for a very long time following the temperature drop and will drop much, much more slowly in response to the cooling. In fact in the cooling part of the cycle the secondary feedback on the warming cycle (water vapour following the CO2 rise) will seem to reduce much more quickly than the primary feedback (the raised atmospheric CO2).

Another way of thinking about this is to recognisie the truism that the earth's equilibrium temperature will fluctuate (by internal variations of the climate system) around a level that is "set" by whatever level of greenhouse gas concentrations and insolation that happens to pertain. However the rates at which these equilibria are attained depends on the rates at which various feedbacks respond. So what might seem to be anomalous phenomena, are not unexpected at all....

Re: "Another way of thinking about this is to recognisie the truism that the earth's equilibrium temperature will fluctuate (by internal variations of the climate system) around a level that is "set" by whatever level of greenhouse gas concentrations and insolation that happens to pertain."
ASSUMPTION!!!

Well that's good Quietman....you don't have a problem with some of the simple expectations of CO2 feedbacks as they apply under the influence of Milankovitch cycles.

On the other hand it's not obvious why you consider a truism to be an assumption! It's been known since the middle of the 19th century that the earth's temperature is defined by the insolation from the sun (which gives the Earth a black body temperature near -15 oC) and the greenhouse effect arising largely from water vapour and CO2 that supplements the black body temperature by around 30 oC.

That's pretty much a truism. One cannot pretend that the greenhouse effect doesn't exist! So the solar and greenhouse contributions effectively set the earth's equilibrium temperature, and stochastic and cyclical variations in the climate system (wind and ocean currents) and volcanic effects, give rise to fluctuations around the equilibrium temperature. Occasionally rather horrible impacts from extraterrestrial sources or catastrophic tectonic events generate major abrupt perturbations. But otherwise it's the sun and the greenhouse effect.

...and indeed the major independent variable with respect to the greenhouse effect is the atmnospheric CO2 (and methane somewhat, especially in the deep past) concentration, since as we all know very well, atmospheric water vapour concentrations rather passively follow the atmospheric temperature (and pressure).